1. Field of the Invention
The invention is related to semiconductor laser based devices for sensing a distance, a displacement, or an image or characteristics of a sample material.
2. Background of the Related Art
Distance and displacement sensing devices that utilize a laser have been known for many years. Typically, the device will output a laser beam that strikes a target object and is reflected from the target object. The reflected laser beam is sensed by a detector, and characteristics of the reflected laser beam are used to determine a distance to the target object, or a displacement of the target object when the object moves.
One such device for determining a distance to a target object is shown in U.S. Pat. No. 5,020,901 to deGroot, the contents of which are hereby incorporated by reference. In the deGroot system, a laser diode emits an amplitude modulated laser beam that is reflected from a target object. The reflected laser beam is sensed by a detector. A signal from the detector provides a measure of the amplitude modulation characteristics of the reflected laser beam, which in turn, is indicative of a position (or change in position) of the target object.
A device for determining a displacement of a target object is shown in U.S. Pat. No. 5,619,318 to Yamomoto et al., the contents of which are hereby incorporated by reference. In one embodiment, the Yamomoto system includes a vertical cavity surface emitting laser that generates a laser beam that is directed toward a target object, and a photodetector located adjacent to the path of the laser beam on the target object. The detector senses characteristics of the laser beam output by the laser. In another embodiment, the detector is located adjacent the laser. In this embodiment, the detector senses characteristics of the laser light output by the laser and reflected from the target object. Characteristics of the sensed laser light are used to determine a displacement of the target object.
The use of vertical cavity surface emitting lasers has become more common in recent years as semiconductor fabrication techniques have become more sophisticated and less expensive. Also, several different structures have been created which combine both a vertical cavity surface emitting laser and a detector on a single substrate. Such laser emitter and detector pairs are described in U.S. Pat. No. 5,285,466 to Tabatabaie, U.S. Pat. No. 5,648,979 to Mun et al., and U.S. Pat. No. 5,491,712 to Lin et al. The contents of all three of these patents are hereby incorporated by reference.
All of these prior art devices require the use of both a laser emitter and a separate detector to determine a distance to a target object or a displacement of a target object.
Two types of known confocal microscope systems are shown in FIGS. 1A and 1B. A confocal microscope system is used to obtain an image or to determine characteristics of a very small portion of a sample material. The device is typically provided with means for scanning an interrogating light beam, or with means for moving the sample material relative to the sensing device, so that the image or characteristics of many different small portions of the sample material can be obtained. This information can then be combined to create an entire image of the sample material, or a map of the sample material's characteristics.
In the confocal system shown in FIG. 1A, a light source 10 outputs light, most of which is blocked by a shutter 12. A small portion of the light passes through a small aperture 11 in the shutter. This essentially creates a point source of light.
The light passing through the aperture 11 is then focused onto a sample material 15 by a focusing lens 14. The focusing lens is controlled to focus the light onto a specific point on the sample material. In the system shown in FIG. 1A, the focusing lens 14 focuses the light onto an interrogated point 13 in a focal plane 16 within the sample material 15. The light passes through the interrogated point and on to a second focusing lens 17. The second focusing lens focuses the light through an aperture in a second shutter 18. Any light passing through the aperture in the second shutter 18 then impinges on a detector 19, which creates an output signal.
The second focusing lens 17 is arranged so that only light passing through the interrogated point will pass through the aperture in the second shutter 18. Thus, any stray light from structures above and below the interrogated point are filtered out. This type of confocal system is able to determine characteristics of an extremely small interrogated point in a sample material.
The sample material can then be moved to interrogate other points in the material, or the interrogating light beam can be scanned across the material to interrogate other points. The most common system is laser scanning, where two or more mirrors are used to sweep the interrogating light beam across the sample material. The intensity of the light beam impinging on the detector is recorded for each point on the sample material, and a complete set of recorded intensities can be used to create an image of the interrogated portions of the sample material. Such a system can be used to determine the characteristics of multiple planes within a three dimensional sample material. Thus, a stack of planar images, or a stack of planar characteristic maps can be obtained.
In the confocal system shown in FIG. 1A, light transmitted through the sample material is used to obtain an image or to determine sample characteristics. The confocal system shown in FIG. 1B uses light reflected from interrogated points in the sample material.
In the system shown in FIG. 1B, light is produced by a light source 10, and the light passes through an aperture 11 in a shutter 12. The light is columnated by a first focusing lens 14a, and the columnated light passes through a beam splitting element 14b. The light then passes through a second focusing lens 14C, which focuses the light on an interrogated point 13 in a focal plane 16 within a sample material 15. Light reflected from the interrogated point 13 passes back through the second focusing lens 14c and on to the beam splitting element, which sends at least a portion of the reflected light toward a third focusing lens 17. The reflected light passing through the third focusing lens 17 is focused through an aperture in a second shutter 18 onto a detector 19.
A device as shown in FIG. 1B can also be used to obtain an image or to determine characteristics of small points within the sample material. This type of confocal system can also include some means for moving the interrogating light beam over different portions of the sample material.